Suspension for wheeled vehicles

ABSTRACT

A wheelchair suspension comprises a frame, at least one pivot arm, at least one front caster, at least one rear caster, a stabilizing system, and a sensor. The pivot arm is coupled to the frame. The front caster is coupled to the pivot arm. The rear caster is coupled to the frame. The stabilizing system is coupled to the frame and the pivot arm. The sensor is arranged such that movement of the frame relative to the rear castor causes actuation of the stabilizing system to at least partially resist further movement of the frame.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH

This invention was not made by an agency of the United States Governmentnor under contract with an agency of the United States Government.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. applicationSer. No. 10/695,045, now U.S. Pat. No. 7,083,195, entitled “Suspensionwith Releasable Locking System” filed on Oct. 27, 2003, which is acontinuation-in-part of U.S. application Ser. No. 10/643,010, now U.S.Pat. No. 6,851,711, entitled “Vehicle Having an Anti-Dive/LockoutMechanism” filed on Aug. 18, 2003, which claims the benefit of U.S.Provisional Application Serial No. 60/421,178 filed on Oct. 25, 2002.U.S. patent application Ser. No. 11/472,509 is also a continuation ofU.S. application Ser. No. 11/077,483, entitled “Self-StabilizingSuspension for Wheeled Vehicles” filed on Mar. 10, 2005, now U.S. Pat.No. 7,293,801. The entire disclosures of the U.S. application Ser. No.11/472,509 and U.S. Pat. Nos. 7,293,801; 7,083,195 and 6,851,711 areincorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates generally to conveyances and, more particularly,to motorized conveyances (vehicles) such as wheelchairs and scooters.

BACKGROUND OF THE INVENTION

Wheelchairs and scooters are an important means of transportation for asignificant portion of society. Whether manual or powered, thesevehicles provide an important degree of independence for those theyassist. However, this degree of independence can be limited if thewheelchair is required to traverse obstacles such as, for example, curbsthat are commonly present at sidewalks, driveways, and other pavedsurface interfaces. This degree of independence can also be limited ifthe vehicle is required to ascend inclines or descend declines.

In this regard, most wheelchairs have front and rear casters tostabilize the chair from tipping forward or backward and to ensure thatthe drive wheels are always in contact with the ground. One suchwheelchair is disclosed in U.S. Pat. No. 5,435,404 to Garin. On suchwheelchairs, the caster wheels are typically much smaller than thedriving wheels and located both forward and rearward of the drivewheels. Though this configuration provides the wheelchair with greaterstability, it can hamper the wheelchair's ability to climb overobstacles such as, for example, curbs or the like, because the frontcasters could not be driven over the obstacle due to their small sizeand constant contact with the ground.

U.S. Pat. No. 6,196,343 to Strautnieks also describes a wheelchairhaving front and rear casters. The front casters are each connected to apivot arm that is pivotally attached to the sides of the wheelchairframe. Springs bias each pivot arm to limit the vertical movementthereof. So constructed, each front caster can undergo vertical movementwhen running over an obstacle.

While the above-mentioned art provides various ways of addressing theneed for stabilizing mid-wheel drive vehicles, a need for furtherstabilization exists. For example, though equipped with front and rearsuspended casters, most mid-wheel drive wheelchairs exhibit variousdegrees of tipping forward or rearward when descending declines orascending inclines. This is because the suspensions suspending the frontor rear stabilizing casters are compromised so that they are not madetoo rigid, which would prevent tipping and also not provide muchsuspension or are made too flexible thereby effectively not providingany degree of suspension or stabilization. Hence, a need exists foraddressing the tipping or “diving” experienced by most mid-wheel drivevehicles that have suspension systems included with their stabilizationmechanisms.

SUMMARY OF THE INVENTION

An embodiment of a wheelchair suspension comprises a frame, at least onepivot arm, at least one front caster, at least one rear caster, astabilizing system, and a sensor. The pivot arm is coupled to the frame.The front caster is coupled to the pivot arm. The rear caster is coupledto the frame. The stabilizing system is coupled to the frame and thepivot arm. The sensor is arranged such that movement of the framerelative to the rear castor causes actuation of the stabilizing systemto at least partially resist further movement of the frame.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which are incorporated in and constitute apart of the specification, embodiments of the invention are illustrated,which together with a general description of the invention given aboveand the detailed description given below, serve to example theprinciples of this invention.

FIG. 1 is a block diagram of a first embodiment of an electronic-basedstabilization system.

FIG. 2 is a block diagram of a second embodiment of an electronic-basedstabilization system.

FIG. 3 is a block diagram of a third embodiment of an electronic-basedstabilization system.

FIG. 4 is a side elevation overview of a first embodiment of amechanically-based stabilization system.

FIG. 5 is a partial perspective view of a second embodiment of amechanically-based stabilization system.

FIGS. 6A and 6B illustrate a first embodiment of a locking member orassembly.

FIGS. 7A and 7B illustrate a second embodiment of a locking member orassembly.

FIGS. 8A, 8B, and 8C illustrate a third embodiment of a locking memberor assembly.

FIG. 9 illustrates a fourth embodiment of a locking member or assembly.

FIGS. 10A, 10B, and 10C illustrate a fifth embodiment of a lockingmember or assembly.

FIGS. 11A and 11B illustrate a sixth embodiment of a locking member orassembly.

FIGS. 12A through 12I illustrate a seventh embodiment of a lockingmember or assembly.

FIGS. 13-18B illustrate an eighth embodiment of a locking member orassembly.

FIG. 19 is a right side elevational view of a portion of a wheeledvehicle with an exemplary stabilization system having a self-aligninglocking member.

FIGS. 20A-20C and 21A-21C illustrate other locking members.

FIGS. 22-28 illustrate another exemplary wheeled vehicle with anexemplary stabilization system having a self-aligning locking member.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT

Generally, a mid-wheel drive wheelchair or scooter is a vehicle used toassist those having an impaired ability to transport themselves. Assuch, the mid-wheel drive wheelchairs and scooters of the presentinvention have at least two drive wheels that are positionedapproximately below the center of gravity of the vehicle when loadedwith a user. This results in a majority of the total wheelchair orscooter weight being on the two drive wheels. Mid-wheel drivewheelchairs and scooters also include one or more casters for forwardand rearward stability, respectively positioned forward and rearward ofthe drive wheels. One example of a mid-wheel drive wheelchair can befound in U.S. Pat. No. 5,435,404 to Garin, which is hereby fullyincorporated by reference.

At least one motor or combination motor/gear box is provided to drivethe drive wheels. The motor is typically controlled by an electroniccontroller connected to one or more user control devices. The usercontrol devices generally provide selection of forward and reversemovement of the vehicle, as well as controlling the velocity or speed. Abattery typically supplies the controller and drive motors with anenergy supply. Dynamic braking and an automatic park brake are alsoincorporated into the vehicle. The dynamic brake allows the operator toproceed safely, even down a slope, without worrying that the vehiclewill unreasonably increase in speed while going down the slope. Further,the park brake automatically engages to hold the vehicle in place whenthe vehicle is standing still.

The present invention provides multiple embodiments of a stabilizationsystem that provides mid-wheel drive vehicles with an anti-dive or lockout mechanism. Generally, the stabilization system includes a trigger orsensor for sensing when conditions exist that may cause the mid-wheeldrive vehicle to exhibit a tipping behavior, which can be either forwardor rearward, and a locking member or assembly that locks the suspensionsystem to prevent any further tipping behavior. The trigger or sensoralso senses when the mid-wheel drive vehicle is no longer subject toconditions that may cause it to exhibit a tipping behavior and causesthe locking member or assembly to no longer lock the suspension system.

Referring now to FIGS. 1 and 4, a block diagram of a first embodiment100 of an electronic-based stabilization system is shown and arepresentative mid-wheel drive wheelchair is shown, respectively.Referring more specifically to FIG. 4, the mid-wheel drive wheelchairhas a frame 402 and pivot arm 404. A pivotal connection 406 connectsframe 402 and pivot arm 404. Attached to pivot arm 404 is a drive wheel410. This attachment is typically provided through a motor or motor/gearbox that is attached to pivot arm 404. Pivot arm 404 further has a frontcaster 412 attached to a forward portion thereof, while the motor ormotor/gear box is attached to a more distal opposite portion. Mountingbrackets and/or apertures are provided in pivot arm 404 for connectingpivot arm 404 to frame 402 via pivotal connection 406. A rear casterassembly 416 is provided that includes a frame member 418 and caster414. A second pivot arm and assembly is similarly provided on theopposite of the wheelchair, as shown in FIG. 5.

Referring now to FIG. 1, the stabilization system triggers a lockingmember or assembly whenever the summation of moments or torque aboutpivotal connection 406 exceeds a pre-loaded value or, in other words,causes the frame 402 of the wheelchair to tip forward. One of the momentarms that influences this loading is the moment arm defined by thedistance from the center of gravity Cg of the mass of the wheelchairoccupant and seat 408 to pivotal connection 406. The torque or momentacting on the center of gravity Cg is generally defined by: (mass of thewheelchair occupant and seat)×[(wheelchair acceleration)+(sine of theslope angle)×(acceleration of gravity)]. The slope angle is the slope ofthe angle measured from a horizontal. For example, if the wheelchair istraveling on a horizontal surface, the slope angle is zero (0) degrees.If the wheelchair is traveling up an incline, the slope angle may be,for example, five (5) degrees. If the wheelchair is traveling down adecline, the slope angle may be, for example, minus five (−5) degrees.As such, the present invention is configured to trigger the lockingmember or assembly sooner when traveling down declines (i.e., negativeslope angle), compared to when traveling up inclines (i.e., positiveslope angle).

As illustrated in FIG. 1, the system 100 includes a controller 101, divelockout control logic 102, and motor/brake logic 103. Controller 101 isany computer-based controller suitable for controlling a vehicle. Inthis regard, controller 102 generally has a processor, memory, andinput/output components (not shown). Controller 101 can also haveelectric motor drive circuitry associated therewith (not shown) thatconnects to drive motors 104 and 106. A user input device 108 such as,for example, a joystick, provides control information to the controller101 for driving the wheelchair. A sensor 126 is provided for sensing theforce acting on the center of gravity Cg of the wheelchair occupant andseat and outputs a signal S to controller 102. As will be presentlydescribed, sensor 126 can be any one of several embodiments. Theremainder of system 100 includes electronic switches 110 and 112, nodes114, 118, and 121, diodes 116 and 120, resistor 122 and solenoid coil124. Solenoid coil 124 is part of an electronic locking member orassembly such that the state of the coil (i.e., energized orunenergized) defines the state of the locking member or assembly (i.e.,locking or not locking the suspension system).

In operation, controller 101 receives driving command inputs fromjoystick 108. This causes controller 101 to output voltages V_(L) andV_(R) and current I_(L) and I_(R) to the left and right motors 104 and106, respectively. Attached to each motor is a motor lock 105 and 107,respectively. All the components of the system are typically powered bybattery having a positive voltage potential B+ and a ground potential“Gnd.” The sensor 126 is mounted on the wheelchair so as to generate atrigger signal S when the wheelchair is tipping forward. In thepresently described embodiment, the trigger signal S is an electronicsignal. In other embodiments, this can be a mechanical signal such asthat generated by a push-pull cable assembly.

Solenoid coil 124 is controlled by the state of electronic switch 112.The locking member or assembly associated with solenoid coil 124 ispreferably in its unlocked state when solenoid coil 124 is energized andin its locked state when solenoid coil 124 is unenergized.Alternatively, the opposite configuration can also be employed.

Nodes 114 and 118 and diodes 116 and 120 form an OR circuit thatcontrols the state of electronic switch 112 and, hence, the energy stateof solenoid coil 124. More specifically, node 114 forms one input to theOR circuit and relates to the state of the motor brakes. For example,when the motors are being driven, the brakes disengage and motor/brakelogic 103 causes node 114 to be at 5V. This, in turn, causes electronicswitch 112 to close thereby energizing solenoid coil 124 and releasingthe locking member or assembly from locking the wheelchair suspension.When the motors are not being driven, the brakes are engaged andmotor/brake logic 103 causes node 114 to be at 0V. This causeselectronic switch 112 to open, which de-energizes solenoid coil 124thereby engaging the locking member or assembly to lock the suspension.

Node 118 forms the second input to the OR circuit and relates to inputprovided by sensor 126 for detecting when conditions may exist thatindicate the wheelchair may start exhibiting a tipping behavior. Morespecifically, if sensor 126 is not indicating that conditions existunder which wheelchair may exhibit a tipping behavior, dive lockoutcontrol logic 102 interprets this state and causes node 118 to be at 5V.This, in turn, causes electronic switch 112 to close thereby energizingsolenoid coil 124 and releasing the locking member or assembly fromlocking the wheelchair suspension. When sensor 126 senses thatconditions exist for a tipping behavior, dive lockout control logic 102interprets this state and causes node 118 to be at 0V. This, in turn,causes electronic switch 112 to open thereby de-energizing relay 124 andengaging the locking member or assembly to lock the wheelchairsuspension.

Illustrated in FIG. 2 is an embodiment 200 of a stabilization systemsimilar to embodiment 100 of FIG. 1. In embodiment 200, the sensor 126(of embodiment 100) includes an accelerometer 204 that produces anacceleration input signal A_(F) to controller 101. Accelerometer 204 canbe any convention accelerometer that provides an output signal that isproportional to the sensed acceleration. In one embodiment,accelerometer 204 can be an appropriately damped pendulum mercuryswitch. In another embodiment, accelerometer 204 can be an electronicaccelerometer such model no. ADXL202 manufactured by Analog Devices ofNorwood, Mass. Accelerometer 204 is preferably located on or near thewheelchair seat proximate the center of gravity Cg of the wheelchairseat and occupant.

The operation of embodiment 200 is substantially the same as embodiment100, except that the state of node 118 is dependent on accelerationsignal A_(F.) The acceleration signal A_(F) is compared by the divelockout control logic 202 to a dive threshold acceleration parameterA_(D), which may be negative (−A_(D)) indicating wheelchairdeceleration. The value of dive threshold acceleration parameter A_(D)can be either calculated based on the weight of the wheelchair andoccupant or determined experimentally with the actual wheelchair and arange of seat occupant weights. As such, dive threshold accelerationparameter −A_(D) is a parameter that is used by the dive lockout controllogic 202 to determine if conditions are present under which thewheelchair may exhibit a tipping behavior. When dive lockout controllogic 202 determines that acceleration signal A_(F) is more negativethan dive threshold parameter −A_(D), it drives node 118 to 0V. Thiscauses electronic switch 112 to open thereby de-energizing solenoid coil124 and causing the locking member or assembly to lock the wheelchairsuspension. Acceleration signal A_(F) is negative when the wheelchair isdecelerating or facing a downward slope or decline. Otherwise, node 118is maintained at 5V thereby causing electronic switch to close. This, inturn, causes solenoid coil 124 to be energized thus releasing thelocking member or assembly from locking the wheelchair suspension.

Referring now to FIG. 3, an embodiment 300 of an electronically-basedstabilization system is shown. Embodiment 300 is substantially similarto embodiment 100, except that sensor 126 includes a motor voltageand/or current sensor, which can be incorporated into controller 101. Inthis regard, controller 101 can incorporate an analog-to-digital (A/D)converter circuit or can include an external A/D circuit. This A/Dcircuit converts analog signals such as, for example, voltage or currentsignals, to digital or binary signals for input into or interpretationby controller 101. Connected therewith, controller 101 also includesdive lockout control logic 302 for interpreting these voltage and/orcurrent signals.

The operation of embodiment 300 is substantially similar to embodiment200, except that dive lockout control logic 302 interprets how hard themotor is being driven and dynamically braked to determine whether thelocking member or assembly will lock or release the suspension system.In this regard, node 114 behaves as earlier described. Node 118 isdriven to 0V when the wheelchair is traveling forward and there is alarge amount of dynamic braking being generated by motors 104 and 106.Node 118 is also driven to 0V if the wheelchair is accelerating hard inthe reverse direction of travel. Otherwise, node 118 is driven to 5V. Asused herein, dynamic braking generally refers to the process by which amotor's windings are short-circuited when the motor is not being drivenso that the residual rotational energy of the motor causes the motor toact as a generator that generates a voltage and current. Byrecirculating the current generated of this configuration, the motordynamically brakes itself. The behavior of node 118, as described above,is further embodied by Equations (1) and (2) below:If (V _(L) +V _(R))>0 and (I _(L) +I _(R))<−I _(D), then output 0V onnode 114  Eq.(1)If (V _(L) +V _(R))<0 and (I _(L) +I _(R))>I _(D), then output 0V onnode 114  Eq.(2)In the above equations, V_(L), V_(R,) I_(L), and I_(R) are theapproximate terminal voltages and currents of motors 104 and 106,respectively. Variable I_(D) is a threshold parameter representing acurrent level that is used to determine when the motors are beingdynamically braked. The value of threshold parameter I_(D) can becalculated based on the motor specification and weight of the wheelchairand occupant or determined experimentally based on the actual wheelchairweight and a range of seat occupant weights. Equation (1) causes node118 to be driven to 0V when the wheelchair is traveling forward((V_(L)+V_(R))>0) and the motors are dynamically braking themselves((I_(L)+I_(R))<−I_(D)). Equation (2) also causes node 118 to be drivento 0V when the wheelchair is accelerating hard in the reverse direction((V_(L)+V_(R))<0) and the motors are not dynamically braking themselves((I_(L)+I_(R))>I_(D)). As described earlier, when node 118 is driven to0V, electronic switch 112 opens thereby causing solenoid coil 124 tode-energize. De-energizing solenoid coil 124 causes the locking memberor assembly to lock the suspension system. Otherwise, node 118 is drivento 5V, which causes electronic switch 112 to close thereby energizingsolenoid coil 124. Energizing solenoid coil 124 causes the lockingmember or assembly to unlock or release the suspension system.Alternatively, energizing solenoid coil 124 can cause the locking memberor assembly to unlock or release the suspension system and de-energizingsolenoid coil 124 can cause the locking member to lock the suspensionsystem.

Referring now to FIG. 4, one embodiment of a mechanically-basedstabilization system is shown. In this regard, a locking member 420,push-pull cable 424, and pivotal rear castor assembly 416 are provided.Push-pull cable 424 has a first conduit portion attached to a bracket430 on rear caster frame member 418 and a second portion attached to alocking member control bracket assembly 432. Push-pull cable 424 alsohas a first cable portion attached to a rear castor pivot bracketportion 428 and a second cable portion attached to a locking membercontrol arm 422.

Locking member 420 is pivotally connected to frame 402 and pivot arm404. This is accomplished through a conventional pivot assembly thatincludes pins or bolts extending through mounting brackets. A secondsimilar locking member and push-pull cable are associated with a secondpivot arm on the other side of frame 402 and identically configured tolocking members 404 and push-pull cable 424.

In this regard, locking member 420 is preferably a lockable springdevice. Examples of such devices include lockable gas or hydraulicsprings that include piston valve assemblies for locking the springs ina predetermined position. Such lockable gas or hydraulic springsinclude, for example, the BLOC-O-LIFT®, STAB-O-MAT®, and STAB-O-BLOC®models of gas springs as manufactured by STABILUS GMBH, Koblenz,Germany. In the preferred embodiment, arm 422 is mechanically linked tothe reciprocating rod that opens and closes the piston valve assembly ofthe locking member 404.

In operation, when rear castor 414 is contacting the driving surface,push-pull cable 424 causes arm 422 to be pulled toward bracket 432. Thisstate causes locking member 420 to be in its unlocked state therebyallowing pivot arm 404 to pivot about pivotal connection 406 as frontcastor 412 traverses bumps and obstacles on the drive surface. However,when the wheelchair begins to exhibit a tipping behavior (e.g., tippingforward), rear caster 414 will pivot about connection 426. Rear castor414 may or may not completely come off of the driving surface. Thiscauses the cable within push-pull cable 424 to displace. Thisdisplacement is translated to arm 422, which begins to separate fromcontrol bracket 432. When arm 422 separates from control bracket 432,the locking member enters the locked state thereby locking pivot arm 404from pivotal motion about connection 406. When the wheelchair returns toits normal position, rear caster 414 pivots back to its normalground-engaging position thereby releasing locking member 420 viapush-pull cable 424. This allows pivot arm 404 to once again pivot aboutconnection 406. Most preferably, the system is configured that ifpush-pull cable 424 breaks, locking member 420 automatically locks pivotarm 404. Additionally, a resilient spring device can be placed betweenrear caster pivot bracket portion 428 and rear caster frame member 418to bias rear caster 414 around connection 426 towards the drivingsurface.

As an alternative to FIG. 4, push-pull cable 424 can be replaced by alimit switch designed to sense the motion of rear caster pivot bracketportion 428 and a solenoid actuator configured to act upon arm 422 uponmovement of the rear caster pivot bracket portion 428 during awheelchair tipping motion. In this regard, one or more wires connect thelimit switch to the solenoid actuator. In yet another alternative,push-pull cable 424 can be replaced with a plurality of mechanicallinkages that provide the same effect on arm 422.

Illustrated in FIG. 5 is another alternate embodiment 500 to that FIG.4. The embodiments of FIGS. 4 and 5 are substantially similar, exceptthat the embodiment of FIG. 5 includes only one locking member 420 thatis associated with both pivot arms 404 and 510. To facilitate thisconfiguration, a link 502 is provided between the pivot arms 404 and510. Link 502 has a first portion 504 that is pivotally connected tofirst pivot arm 404 and a second portion 506 that is pivotally connectedto second pivot arm 510. Link 502 also has a third portion that ispivotally connected to a bottom portion of locking member 420. A topportion of locking member 420 is pivotally connected to frame 402.Though not illustrated, a push-pull cable mechanically links lockingmember 420 to rear caster 414 or its parallel equivalent in the samefashion as that shown in FIG. 4. The operation of embodiment 500 issimilar to that described for FIG. 4, except that when locking member420 is in the locked state, it prevents link 502 from displacement.This, in turn, prevents either pivot arm 404 or 510 from movement.

Referring now to FIGS. 6A and 6B, an embodiment 600 of a stabilizationsystem having ratchet-type locking member or assembly 602 is shown. Thelocking member 602 has a pawl member 614, ratchet member 620, and asolenoid actuator 608. Pawl member 614 and solenoid actuator 608 arerigidly fixed to frame 402 via a bracket 606. Bracket 606 also serves asa guide bracket for ratchet member 620, though this function can beprovided by a separate guide member. Solenoid actuator 608 has a coil124, spring 612 and pin 613. Pawl member 614 has a first portionpivotally connected to bracket 606 and a second portion pivotallyconnected to pin 613. Ratchet member 620 has a plurality of cammedextensions 622 between which pawl member 614 is configured to engage anddisengage. A bottom portion of ratchet member 620 is pivotally connectedto pivot arm 404 at connection 604. So configured, ratchet member 620 isfree to undergo reciprocating movement within the guide portion ofbracket 606 as pivot arm 404 pivots about connection 406. As describedearlier, solenoid actuator 608 can be controlled by any of theembodiments of FIGS. 1-4.

As such, when the wheelchair exhibits a tipping behavior, solenoidactuator 608 is de-energized causing spring 612 to urge pin 613 and pawlmember 614 against ratchet member 620. This causes pawl member 614 to belocked against ratchet member 620 so as to prevent ratchet member 620from any further upward motion, which causes tipping of the wheelchair.This state prevents the forward portion of pivot arm 404 from exhibitingany upward motion that is associated the wheelchair's tipping behavior.However, it may be desirable to allow ratchet member 620 to further movein the downward direction while pawl member 614 remains engagedtherewith. This is accomplished by appropriately camming the engagingsurfaces of pawl member 614 and ratchet member 620, as shown. In thismanner, pivot arm 404 is free to move in a direction that would lessenthe tipping behavior of the wheelchair but not increase such behavior.If the wheelchair is not exhibiting a tipping behavior or has ceased toexhibit a tipping behavior, solenoid actuator 608 is energized causingpin 613 and pawl member 614 to disengage from ratchet member 620. Thisallows pivot arm 404 to freely pivot about connection 406. As describedearlier in connection with FIGS. 4 and 5, one or two or more lockingmembers can be provided. Additionally, pawl member 614 can be triggeredby a inertial switch or method instead of solenoid actuator 608 or onewhich actuates a solenoid actuator.

Referring now to FIGS. 7A and 7B, an embodiment 700 of a stabilizationsystem having a caliper-type locking member or assembly 702 is shown.The locking member 702 has a spring 712, pin 714, one or more frictionplates 710, and a linear reciprocating link 704. Pin 714 has a firstportion connected to friction plate 710 and a second portion connectedto either a solenoid actuator or push-pull cable, or equivalent, asdescribed earlier for locking and unlocking the suspension system.Spring 712 is located between these portions and biases pin 714 andfriction plate 710 toward link 704. The friction plates 710, spring 712,and pin 714 are housed within a frame attachment 708, which rigidlyconnects these components to frame 402. Attachment 708 also functions asa guide for link 704 so as to always maintain link 704 between frictionplates 710. This function can also be provided by a separate guidebracket.

Link 704 has a first portion that is pivotally connected to pivot arm404 and a second portion that travels within attachment or guide 708 soas to be engagable by friction plates 710. In this manner, as pivot arm404 rotates about connection 406, link 704 exhibits a reciprocating upand down motion with respect to attachment 708 and friction plates 710.Preferably, two friction plates 710 are provided facing each other witha gap therebetween. The space or gap exists between friction plates 710so as to allow link 704 to freely move therethrough until such time asthe friction plate 710 connected to pin 714 is moved toward link 704 andthe opposing friction plate 710. This movement causes both frictionplates 710 to engage the link 704 and to lock it in position. This, inturn, prevents pivot arm 404 from pivoting about connection 406. Hence,when the wheelchair is exhibiting a tipping behavior, pin 714 isextended allowing friction plate 710 to engage against link 704. Whenlink 704 is locked between friction plates 710, the wheelchair will notexhibit any tipping behavior. When the conditions for a tipping behaviorare absent, pin 714 is in its retracted position and link 704 can movefreely between friction plates 710.

Referring now to FIGS. 8A, 8B, and 8C, an embodiment 800 of astabilization system having a magnetic-field actionable locking memberis shown. Referring specifically to FIG. 8C, embodiment 800 has alocking member 804 and an actuator assembly 802 associated therewith.Locking member 804 has a first portion 806 that is pivotally connectedto pivot arm 404 and a second portion 808 that is pivotally connected toframe 402. Locking member 802 is a hydraulic piston assembly having amagnetic fluid. The piston within the assembly has a valve that allowsthe fluid to pass from one side of the piston to the other. However,when a magnetic field is brought near the proximity of the fluid, themagnetic field causes the fluid viscosity to greatly increase therebynot allowing the fluid to flow through the valve in the piston. This, inturn, locks the piston in position.

Illustrated in FIG. 8A is a first embodiment of the actuator assembly802. The assembly 802 has a permanent magnet 810 that is fixed directlyor indirectly to frame 802, a solenoid coil 812 and a switch 814.Solenoid coil 812 can be the same component as solenoid coil 124 andswitch 814 can be mechanical or electronic, as described in connectionwith FIGS. 1-4. In operation, magnet 810 causes the fluid in lockingmember 804 to have a very high viscosity and, hence, almost no abilityto flow. This maintains locking member 804 in a locked stated therebylocking pivot arm 404 from pivoting about connection 406. However, whensolenoid coil 812 is energized by switch 814, its magnetic field cancelswith the magnetic field generated by magnet 810 and allows the fluid inlocking member 812 to have a very low viscosity and, hence, the abilityto flow relatively easily. This allows locking member 804 to move inaccordance with the movement of pivot arm 404 about pivotal connection406. Hence, if power is lost, magnet 810 provides a failsafe conditionwhich automatically locks locking member 804. Therefore, it can be seenthat when the wheelchair exhibits a tipping behavior, solenoid coil 812is de-energized causing locking member 804 to lock pivot arm 404. Whenno tipping behavior is exhibited by the wheelchair, solenoid coil 812 isenergized and locking member 804 is not in its locked state.

Illustrated in FIG. 8B is a second embodiment of an actuator assembly802. This embodiment has the earlier described push-pull cable 424spring-loaded against magnet 810. In this embodiment magnet 810 moveseither toward or away from the locking member 804 so as to either bringits magnetic field in operative proximity to the locking member or awayfrom the locking member. As described in connection with FIG. 4,push-pull cable 424 provides for linear mechanical movement upon atipping condition of the wheelchair. By having push-pull cable 424 fixedto magnet 810, the linear movement of push-pull cable 424 can be used tomove magnet 810 closer to locking member 804 so as place it in itslocked state, or away from locking member 804 so as to place it in itsunlocked state. Spring is also provided so as to bias magnet 810 towardslocking member 804 ensuring that locking member 804 is in its lockedstate should push-pull cable 424 break.

Referring now to FIG. 9, an embodiment 900 of a suspension system havinga sprag clutch locking member 902. Sprag clutch locking member 902allows rotational movement in one direction and not in the other.Alternatively, locking member 902 can be a bi-directional clutch.Bi-directional clutches allow their input to drive their output ineither rotational directions, but do not allow the output to drive theinput.

FIGS. 10A, 10B and 10C illustrate one embodiment 1000 of a suspensionsystem having a direct acting pin locking member 1002. Locking member1002 extends and retracts its pin 1008 so as to enter one of a pluralityof slots or apertures in locking bracket 1004. In this regard, lockingmember 1002 has a spring-loaded pin 1008 and an actuator cable 1006. Iflocking member 1002 is mechanical, then actuator cable 1006 can be apush-pull cable, as described earlier. If locking member 1002 issolenoid driven, then actuator cable 1006 can be an electric cable thatcarries the signal that actuates the solenoid. The locking member 1002can also be pneumatically actuated through known means. So configured,locking member 1002 is affixed to the frame 402 through mountingbrackets (not shown) or its housing.

Locking bracket 1004 is affixed to pivot arm 404 and moves therewith. Inthis regard, locking bracket 1004 preferably includes an arcuate shapeso as to maintain alignment with locking member 1002 as pivot arm 404pivots or rotates. Locking bracket 1004 includes a plurality ofapertures or slots that disposed along the bracket's arcuate body. Theapertures can be any shape such that pin 1008 can enter thereinto. Pivotarm 510 (not shown) would have a similar suspension system.

Illustrated in FIG. 10C is detail of an alternative embodiment of pin1008. More specifically, FIG. 10B shows pin 1008 having flat headportion at its engaging distal end. FIG. 10C shows an embodiment of pin1008 having a cammed surface 1010 at its engaging distal end. Cammedsurface 1010 is provided so that when pin 1008 is engaged in lockingbracket 1004, pivot arm 404 can pivot in the downward direction. Thiscauses a ratcheting effect where cammed surface 1010 causes pin 1008 toretract under the downward tendency (i.e., clockwise rotation) of pivotarm 404. However, configured as such, pin 1008 does not allow acorresponding ratcheting in the upward direction (i.e.,counter-clockwise rotation) of pivot arm 404.

In operation, pin 1008 of locking member 1002 is spring-engaged into anaperture of locking member 1004. Actuator cable 1006, when active,causes pin 1008 to retract from locking bracket 1004. In this manner, afailsafe configuration is provided should actuator cable 1006 fail. Thetriggering of locking member 1002 can be by any of the embodimentsdescribed in FIGS. 1-4.

Illustrated in FIGS. 11A and 11B an embodiment 1100 of a suspensionsystem having an axial spring locking member 1002. In particular,locking member 1102 has an actuator member 1108. Actuator member 1108can be a spring-loaded pin, solenoid driven pin, or a mechanical clamp(not shown). Actuator member 1108 is actuated by an actuator cable 1110,which can be an electric cable, pneumatic hose, or push-pull cable.Locking member 1102 further has a housing 1112 that includes a spring1113 that axially receives a locking rod or tube 1106 therein. Lockingmember 1102 is rigidly affixed to frame 402 with mounting brackets (notshown).

Spring 1113 is a coil spring that includes first and second extensions1114 and 1116, respectively. Spring 1113 is arranged so that whenextensions 1114 and 1116 are not acted upon by any force, spring 1113 istightly coiled around locking rod or tube 1106 so as to prevent anyaxially movement of locking rod or tube 1106 within spring 1113. Sincelocking rod or tube 1106 has one of its distal ends pivotally fixed topivot arm 404 at 1104, pivot arm 404 is also locked from any rotationalmovement. In this manner, a failsafe configuration is provided shouldactuator cable 1110 fail. The triggering of locking member 1102 can beby any of the embodiments described in FIGS. 1-4.

To release locking rod or tube 1106 from spring 1113, extensions 1114and 1116 are acted upon by a force. In this regard, extensions 1114 and1116 can be configured so that either a force that brings them closertogether or a force that brings them farther apart causes spring 1113 tobecome loosely coiled around locking rod or tube 1106. Once looselycoiled, spring 1113 allows locking rod or tube 1106 to axially movetherein. This, in turn, allows pivot arm 404 to pivot about itsconnection at 403. Pivot arm 510 (not shown) would have a similarsuspension system.

Referring now to FIGS. 12A, 12B, 12C, 12D, and 12E, an embodiment of asuspension system 1200 having an linear locking member 1202 is shown.FIG. 12A shows the suspension system on a level driving surface. FIG.12B illustrates the suspension system wherein front caster 412 is liftedby the suspension off of the driving surface. FIG. 12C shows thesuspension system wherein front caster 412 has been lowered onto a lowerdriving surface. FIG. 12D illustrates the suspension 1200 with the drivewheel removed and FIG. 12E is a partial perspective view of thesuspension 1200.

Suspension system 1200 further includes a four-bar pivoting assemblythat includes pivot arms 1204A and 1204B, caster head tube bracket 1214,and frame 402. Bracket 1208, while a separate component, can beconsidered as part of frame 402. Pivot arms 1204A and 1204B arepivotally connected to frame 402 via pivotal connections 1206A and1206B. Pivot arms 1204A and 1204B are also pivotally connected casterhead tube bracket 1214 via pivotal connections 1207A and 1207B.

Locking member 1202 is shown having a first pivotal connection 1210 topivot arm 1204B and a second pivotal connection 1212 to bracket 1208. Soconnected locking member is under the influence of pivot arms 1204A and1204B. It should be noted that locking member 1202 pivotal connection1210 can be alternatively located on pivot arm 1204A or caster head tubebracket 1214, as well.

FIG. 12F illustrates a partial cross-section of locking member 1202.Locking member 1202 has a first housing 1220 and a second housing 1222.First housing 1220 retains therein a electric solenoid actuator 1230that includes a coil and a plunger 1232 biased by leaf spring 1228. Acover 1226 is provided on housing 1220 that has an aperture that allowsplunger 1232 to at least partially project there from. The projectingportion of plunger 1232 has a pivotable lever 1224 connected thereto.Pivoting of the lever through manual actuation causes plunger 1232 tomove without the need for electrical energy.

Second housing 1222, which is attached to first housing 1220 includes achannel or passage 1234 therein. A rod member 1236 moves within passage1234 and includes a notch 1238 therein. Notch 1238 is configured suchthat when plunger 1232 is biased into passage 1234, plunger 1232 willcome into locking engagement with notch 1238 and remain there untilwithdrawn. Alternatively, notch 1238 can be replaced by a ratchetingtooth configuration similar to that shown in FIG. 6B.

Referring now to FIGS. 12G and 12H, perspective and top views of lockingmember 1202 are illustrated. Rod member 1236 includes at one distal endan aperture 1240, which accepts a pin or similar fastener in formingpivotal connection 1210. Additionally, second housing 1222 includes atone distal end first and second extensions 1246 and 1248, each of whichhave aligned apertures 1244. Extension 1246 and 1248 accept in the spacebetween them a pivoting bracket member that is used secure the lockingmember 1202 to bracket 1208.

Illustrated in FIG. 121 is an exploded perspective view of lockingmember 1202. In addition to the above-mentioned components, lockingmember 1202 further includes a block 1252 that is affixed to plunger1232. Block 1252 increases the effective cross-section of plunger 1238which is responsible for locking engagement with rod member 1236.Housing 1222 has a cover portion 1250 that includes an aperture 1254having substantially the same shape as block 1252 and allows block 1252to reciprocate there within.

In operation, locking member 1202 locks the suspension system when, forexample, the vehicle is not moving and motor parking brake or lock isactuated. This creates a stable platform for the user to transport inand out of the vehicle or wheelchair. Locking member 1202 is alsopreferably configured to lock suspension system when the is no power orthe power system has been shut off. This is achieved by always biasingplunger 1232 into locking engagement with rod member 1236. Uponpower-up, solenoid 1230 is actuated and plunger 1232 is withdrawn fromthe locking engagement.

So configured, locking member 1202 can be alternatively located among aplurality of positions the on suspension system 1200. For example,locking member 1202 can be attached between the frame 402 and upperpivot arm 1204A, attached between the upper and lower pivot arms 1204Aand 1204B, or between any two components of the described four-barpivoting assembly. Additionally, locking member 1202 can be triggered byany of the mechanisms described earlier electrical or mechanical.

Illustrated in FIG. 13 is an eighth embodiment of a locking assembly ofthe present invention. The locking assembly has a motor rack bracket1314, first ratchet 1320, second ratchet 1322 and a spring mount 1318.So configured, the locking assembly is shown mounted on the vehicleframe 402, which includes a four-bar linkage pivoting front casterassembly. The four-bar linkage pivoting caster assembly includes firstand second linkages 1302 and 1304. A third linkage is provided by frame402 and its extension in the form of frame bracket 1306. A fourthlinkage is provided by caster head tube assembly 1311. First linkage1302 is pivotally connected to frame 402 at pivot 1310 and secondlinkage 1304 is pivotally connected to frame 402 at pivot 1308. A moredetailed discussion of this four-bar linkage pivoting front casterassembly can be found in pending U.S. patent application Ser. No.09/974,348, filed on Oct. 10, 2001, which is hereby fully incorporatedby reference.

The locking assembly's motor rack bracket 1314 is physically connectedto first linkage 1302 through a motor/gearbox mount 1312. The connectioncan also be made directly if desired. A gearbox 1316 is also shownconnected to motor/gearbox mount 1312. First ratchet 1320 is attached tomotor rack bracket 1314 at an end portion opposite the connection tofirst linkage 1302. So configured, motor rack bracket 1314 pivots whenfirst linkage 1302 pivots.

The locking assembly's spring mount 1318 is pivotally connected to frame402 through clevis 1325. The second ratchet 1322 is affixed to a sideportion of the spring mount 1318. Clevis 1325 and its pivotal connection1324 allow spring mount 1318 to pivot with respect to frame 402. In analternate embodiment, pivotal connections 1324 and 1332 and devises 1325and 1334 can be combined into a single integrated clevis and pivotalconnection. For example, clevis 1325 can be eliminated and pivotalconnection 1324 integrated into pivotal connection 1332.

In another embodiment, an elastic member such as, for example, a spring,can be positioned between spring mount 1318 and frame 402. Such a springwould urge or assist the pivotal movement of spring mount 1318 away fromframe 402, as will be described below. To facilitate such a spring,spring mount 1318 would include a bearing surface for bearing againstone end of the spring and a spring holder. This configuration can takethe form of pin or bolt at least partially received within the spring,which such configuration may additionally be at least partially receivedwithin a recess in spring mount 1318. The other end of the spring wouldbear against a bearing surface on frame 402. Alternatively, such aconfiguration can be reversed between the spring mount 1318 and frame402.

A rear caster mount 1328 pivotally connects rear caster 414 to frame402. More specifically, rear castor mount 1328 has an extension 1330that includes a first distal end pivotally connected to clevis 1334 anda second distal end connected to a head tube portion for mounting therear caster 414. A spring 1326 is situated between rear castor mount1328 and spring mount 1318. Spring 1326 compresses when rear castermount 1328 pivots clockwise as shown in FIG. 13 toward frame 402. Inthis manner, spring 1326 provides a degree of suspension for the rearcaster mount 1328. Alternatively, if no degree of suspension is desired,spring 1326 can be replaced by a non-resilient member resulting inspring mount 1318 and rear caster mount 1328 being an integrated andrigid structure. As described above, such an integrated structure canemploy a single integrated pivot at pivotable connection 1332, asopposed to pivotable connections at 1324 and 1332.

In operation, first and second ratchets 1320 and 1322 engage each otherin one of a plurality of releasable locking states whenever rear caster414 is about to be lifted from its supporting surface. This conditionoccurs whenever the frame 402 pivots or tilts forward toward frontcaster 412. When frame 402 pivots or tilts forward, first and secondpivot arm linkages 1302 and 1304 correspondingly pivot about theirpivotal connection 1310 and 1308, respectively. Any pivotal movement oflinkages 1302 or 1304 translates to pivotal movement of motor rackbracket 1314 and first ratchet 1320 by virtue of their mechanicalcoupling. As this condition occurs, rear caster mount 1328 pivots aboutits pivotal connection at 1332 causing spring mount 1318 to pivot aboutits pivotal connection at 1324 so that second ratchet 1322 comes intocontact with first ratchet 1320. When first and second ratchets 1320 and1322 come into contact forming a releasable locking state, pivot armlinkages 1302 and 1304 are releasably locked thereby locking frame 402from any additional pivoting or tilting forward. When frame 402 resumesits normal level position, rear caster mount 1328 pivots clockwisecausing spring mount 1318 to pivot clockwise and disengage secondratchet 1322 from first ratchet 1320. This releases first and secondpivot arm linkages 1302 and 1304 from their locked state so that theymay once again freely pivot.

FIGS. 14 through 16, further illustrate the locking assembly and itscomponents in perspective views. In particular, FIG. 15 is a perspectiveview of the spring mount 1318. Spring mount 1318 further has a surface1502 for bearing against spring 1326 and a structure 1504 holding spring1326 in position relative spring mount 1318. FIG. 16 is a perspectiveview of rear caster mount 1328. Rear caster mount 1328 further has asurface 1602 for bearing against spring 1326 and a structure 1604 forholding spring 1326 in position relative to rear caster mount 1328.

Referring now to FIGS. 17A and 17B, elevational and perspective views,respectively, of the second ratchet 1322 are illustrated. Second ratchet1322 has a body 1702 that includes a plurality of mounting apertures1706 that are used to fasten it to spring mount 1318. Body 1702 alsoincludes a toothed surface 1704. The toothed or undulating nature ofsurface 1704 is configured to provide a plurality of releasable lockingstates when engaged with first ratchet 1320. The number of releasablelocking states can vary from 1 to 2 or more. For example, surface 1704can have a single tooth any where along its length for engagement withfirst ratchet 1320. Additionally, surface 1704 can have first and secondteeth disposed at the proximal ends of its curved or arcuate length.This configuration provides two locking states that permit a range oftipping motion by the frame, but place limits on the range. In yetanother embodiment, surface 1704 can have first and second teethdisposed at the proximal ends of its length and at least one toothsomewhere intermediate the ends. This configuration provides two lockingstates that permit a range of tipping motion by the frame, but whichplace limits on the range, and a third discrete locking stateintermediate the limits. As further illustrated in FIGS. 17A and 17B,surface 1704 is slightly curved or arcuate to compensate for the natureof the pivotal motion first ratchet 1320 experiences as it pivots withpivot arm linkages 1302 and 1304.

FIGS. 18A and 18B are elevational and perspective views, respectively,of first ratchet 1320. First ratchet 1320 has a body 1804 that includesa plurality of mounting apertures 1806, which are used to fasten firstratchet 1320 to motor rack bracket 1314. Body 1804 also has a toothedsurface 1804, which is slightly curved or arcuate to accommodate thepivotal motion experienced by second ratchet 1322. The toothconfiguration of surfaces 1804 and 1704 are configured such thatrelative motion between first and second ratchets 1320 and 1322 is moreor less permitted in one direction, but motion in the opposite directionis impeded.

Also, as described above in connection with second ratchet 1322, thetoothed or undulating nature of surface 1804 is configured to provide aplurality of releasable locking states when engaged with first ratchet1320. The number of releasable locking states can vary from 1 to 2 ormore. For example, surface 1804 can have a single tooth any where alongits length for engagement with second ratchet 1322. Additionally,surface 1804 can have first and second teeth disposed at the proximalends of its curved or arcuate length. This configuration provides twolocking states that permit a range of tipping motion by the frame, butplace limits on the range. In yet another embodiment, surface 1804 canhave first and second teeth disposed at the proximal ends of its lengthand at least one tooth somewhere intermediate the ends. Thisconfiguration provides two locking states that permit a range of tippingmotion by the frame, but which place limits on the range, and a thirddiscrete locking state intermediate the limits.

Some of the exemplary vehicle stabilization systems described above maybe modified. For example, one or more locking members may be movablyconnected to a respective pivot arm or assembly permitting one or bothlocking members to automatically align with the other locking member asthey engage to lock the pivot arms or assemblies to limit furthermovement of the frame in at least one direction. One or more of suchself-aligning locking members may permit solid engagement betweenlocking members during much of the life of the vehicle, even ascomponents of the vehicle wear and/or are deformed over time or as aresult of collisions. The self-aligning locking member(s) may optionallybe “floating” (e.g., freely movable in at least one direction ororientation) with respect to a respective pivot arm or assembly. Theself-aligning locking member(s) may optionally include positional memorysuch that the relative position of the movable locking member(s) duringan engagement with the other locking member with respect to at least oneorientation or direction will be maintained after disengagement, butwill also permit the movable locking member(s) to self-align in thatdirection for the next engagement, if necessary. Such a positionalmemory may be provided by a biasing member (e.g., a spring or a plasticmaterial) operatively connected to bias the locking member against asurface to provide positional memory to the locking member relative toits respective assembly.

For example, referring back to FIGS. 17A-B and 18A-B (and the text andother figures accompanying that embodiment), first ratchet 1320 may bemovably connected to motor rack bracket 1314 and/or second ratchet 1322may be movably connected to spring mount 1318. This may be accomplished,for example, by having any one or more bores used to fasten firstratchet 1320 to motor rack bracket 1314 and/or fasten second ratchet1322 to spring mount 1318 be formed as slots or formed as boressignificantly larger than fasteners passing therethrough. Additionally,or in the alternative, fasteners movably connecting the first ratchet1320 to the motor rack bracket 1314 and/or fasteners movably connectingthe second ratchet 1322 to the spring mount 1318 may be shoulder screwsthat when mounted permit a gap between the first ratchet 1320 and themotor rack bracket 1314 and/or a gap between the second ratchet 1322 andthe spring mount 1318, which permits significant freedom of movement ofthe first ratchet 1320 and/or second ratchet 1322. The first ratchet1320 and/or second ratchet 1322 may have positional memory (e.g.,provided by a spring or other biasing member) in any one or moredirections or orientations and may be “floating” in any one or moredirections or orientations, as discussed herein.

As another exemplary modification, one or more pivot arms or assembliesmay have an associated link pivotally connected to the frame,operatively connected to at least one pivot arm, and operativelyconnected to the associated locking member. Such a link may cooperatewith the at least one pivot arm to cause the first locking member toengage the second locking member responsive to movement of the framerelative to at least one of the first and second assemblies. The use ofsuch a link may permit a relatively wide spacing between the lockingmembers, e.g., spaced apart by ⅜ of an inch or more (e.g., a half-inchor more) when the vehicle is at rest on a flat, level surface. Such alink may also permit exaggerated movement of the locking membersresponsive to movement of the at least one pivot arm, e.g., responsiveto a specific angular movement of the pivot arm causing a greaterangular movement of the link and perhaps other links to movecorresponding locking members toward each other, which may permitgreater sensitivity.

As yet another example, the geometry of the locking members may be suchthat one locking member is longer than the other and has a concavelocking surface. Any combination of any two or more of these additionalfeatures—self-aligning locking members, a link, and/or differentgeometry—may be combined in a vehicle.

Referring now to FIG. 19, a portion of another exemplary wheeled vehicleis shown as having a stabilization system with a self-aligning lockingmember, a link, and locking members with different geometry. Thisexemplary embodiment includes an “anti-dive” stabilization system or“stability lock” that works in combination with the frame of thewheelchair to prevent the chair from tipping over in a forward directionunder certain circumstances. Thus, FIG. 19 shows an exemplary suspension1900 for a wheeled vehicle, comprising a frame 1911, a first assembly1904 movably connected to the frame 1911, a second assembly 1906 movablyconnected to the frame 1911, a first locking member 1930 movablyconnected to the first assembly 1904, and a second locking member 1912connected to the second assembly 1906. In the exemplary suspension 1900shown, movement of the frame 1911 relative to the at least one of thefirst and second assemblies 1904, 1906 causes the first and secondlocking members 1912, 1930 to engage one another (here, the secondlocking member 1912 is moved toward the first locking member 1930 sothat the first locking member 1930 engages the second locking member1912) to permit the first and second assemblies 1904, 1906 to cooperateto limit further movement of the frame 1911 in at least one direction.The first locking member 1930 automatically aligns with the secondlocking member 1912 as the locking members 1912, 1930 engage. FIGS.20A-20C show various views of locking member 1912, which has a generallyconcave shape at toothed surface 1913 that engages the other lockingmember 1930. FIGS. 21A-21C show various views of locking member 1930,which is movably connected to the first assembly 1904. Referring back toFIG. 19, the second assembly 1906 is shown as having an associated link1914 that is pivotally connected to the frame 1911, operativelyconnected to pivot arm 2102, and operatively connected to the lockingmember 1912. Such a link 1914 cooperates with the at least one pivot arm2102 to cause the locking members 1912, 1930 to engage each otherresponsive to movement of the frame 1911 relative to at least one of thefirst and second assemblies 1904, 1906. The suspension of FIG. 19 may beused with an electric wheelchair, such as the Invacare M94 wheelchair orthe Invacare TDX wheelchair (Invacare Corporation, Elyria, Ohio), bothof which utilize frames that include multiple pivot points.

Referring now to FIGS. 22-28, various views of a wheelchair base havingthe suspension of FIG. 19 are shown. As shown in these figures, thisembodiment includes a self-aligning “anti-dive” stabilization system1910. In FIGS. 22-28, the upper portion of the exemplary wheelchair,including the seat and outer shroud, has been removed to better showrelevant structural components. FIG. 22 is a semi-exploded,front-right-top isometric view of the exemplary wheelchair base, with amotor, gear box, and drive wheel exploded to show certain relationshipsbetween various components.

The exemplary wheelchair base of FIGS. 22-28 comprises a frame 1911. Asbest shown in FIG. 22, frame 1911 includes left and right side portions1950, a front portion 1951, a rear portion 1952, shroud mountingbrackets 1954, and a front support bracket 1955. First and secondassemblies 1904, 1906 (FIG. 19) are pivotally connected to the left andright sides of frame 1911 respectively, and each assembly 1904, 1906includes an associated surface-engaging portion. As shown in FIGS. 19and 22-28, the assemblies 1904, 1906 comprise front pivot arms 1956 andrear pivot arms 2102. The front pivot arms 1956 each have an associatedfront caster 2104 and the rear pivot arms 2102 each have an associatedrear caster 2100. The front pivot arms 1956 and the rear pivot arms 2102are both pivotally connected to frame 1911 to increase overallmaneuverability when the wheelchair travels across uneven surfaces orencounters street to curb interfaces or steps. The various attachmentsor connections described herein may accomplished with appropriatemounting screws, shoulder screws or similar attachment means, or byusing other methods and devices known and accepted by those skilled inthe art. Certain components are attached to one another by known weldingtechniques.

As shown in the figures, a swing arm bracket 1960 is used to attach eachpivot arm 1956 to frame 1911 at pivot point A. A torsion spring 1965mounted between pivot arm 1956 and frame 1911 biases the frame to therear (counterclockwise from the perspective of FIGS. 19 and 23). Eachpivot arm 1956 may have an associated stabilization bar 1957 pivotallyattached to the frame below and substantially parallel to the pivot arm1956 to help keep front caster 2104 in a substantially vertical positionas the pivot arm 1956 pivots about point A when the wheelchair is inuse. This configuration is known as a “four bar linkage.” A motorbracket 1962 may be attached to or formed as part of each front pivotarm 1956.

As shown in FIG. 22, an electric motor 1990 may be mounted on motorbracket 1962. A drive wheel 1980 may be mounted on each motor 1990 byattaching the drive wheel 1980 to axle 1992 of the motor or anassociated gear box. The motors 1990 are operated by an electroniccontroller which is connected to one or more user control devices (notshown in the Figures). The user control devices generally provideselection of forward and reverse movement of the vehicle, as well ascontrolling the vehicle's velocity or speed. A battery 1972 is seated intray 1963, held in position (kept from sliding from side to side) withbattery brackets 1959, and secured with a strap. The battery 1972typically supplies the various electric components with an energysupply. In the exemplary embodiment shown in the figures, each of thestabilization systems 1910 is installed between a drive wheel 1980 andthe portion of base assembly 1911 that supports the electroniccomponents of the wheelchair (see FIG. 27-28) and does not interferewith the placement or operation of other system components such as wirewrap 1970, battery 1972, charger 1974, battery handle 1976 and terminalcovers 1977 and 1978. The drive wheels 1980 may be positioned relativeto the frame 1911 so that most (e.g., greater than 50%) of the weight ofthe user of the wheelchair is directly over the drive wheels 1980. Eachfront pivot arm 1956 may operate independently of the other front pivotarm and each allows its associated front caster 2104 and drive wheel1980 to move with the pivot arm 1956 as the pivot arm pivots about pointA when the wheelchair moves across an uneven surface.

As best shown in FIGS. 19 and 23-24, each rear pivot arm 2102 may bepivotally attached to each side frame portion 1950 at the rear portionof frame 1911. Each rear pivot arm 2102 is operatively connected to aframe-mounted pivot bracket 1958, which allows rear pivot arm 2102 topivot around pivot point B. A tube 1966 is welded to each rear pivot arm2102 to confer lateral stability to the arm. If the wheelchair tipsforward, each rear pivot arm 2102 will drop (i.e., rotatecounterclockwise around pivot point B from the perspective of FIGS. 19and 23-24) and each rear caster 2100 will drop or move in a downwarddirection. A stop, e.g., a plastic pad 1969, may be mounted on bothsides of the frame between the rear pivot arm 2102 and the frame 1911.Also, as shown in FIG. 19, a reinforcement flange 1967 adds structuralstability to the two sections of each rear pivot arm 2102. As with frontpivot arms 1956, each rear pivot arm 2102 pivots independently of theother rear pivot arm when the wheelchair moves across an uneven surface.

As best shown in FIGS. 19, 20A-20C, 21A-21C and 25, self-aligningstabilization system 1910 comprises, on each side of the wheelchair, alocking apparatus. Each locking apparatus further includes a pivotinglocking member 1912 having a toothed surface 1913 and a floating lockingmember 1930 having a toothed surface 1931. Toothed surfaces 1913 and1931 engage one another under certain operating conditions to preventthe wheelchair from tipping over in a forward direction, as discussed inmore detail below.

With reference to FIGS. 19 and 20A-20C and 21A-21C, each lockingapparatus of stabilization system 1910 includes a pivoting lockingmember 1912, also referred to as a “pivot rack” connected to or mountedon each side of the outer portion of the frame, and a floating lockingmember 1930, also referred to as a “motor rack,” connected to or mountedon each of the front pivot arms 1956. Each of these locking membersincludes a substantially solid body manufactured from metal or othersuitably rigid and durable material that includes on one of its sides atoothed or ratcheted surface. When properly installed, the toothedsurfaces of each locking member face one another and when stabilizationsystem 1910 is in operation, these teeth engage one another or “lock”together to prevent further movement the components to which the lockingmembers are attached.

In the exemplary embodiment, each pivot rack 1912 typically includes anelongated piece of metal having slightly curved or arced front and rearedges (see FIG. 21A-C). The toothed edge of pivot rack 1912 is slightlyconcave and includes the aforementioned ratchets or teeth. The toothededge 1913 of pivot rack 1912 has a cross-sectional shape substantiallylike a section of a hypothetical circle, with the radius of thehypothetical circle being approximately the same length as a linesegment (not shown) extending from a point (not shown) on pivot point Ato a point (not shown) on the toothed surface 1932 of the other lockingmember 1930. As shown in FIG. 25, pivot rack 1912 is attached topivoting link 1914 with screws 1916 and 1918. Pivot rack 1912 may berigidly attached to pivoting link 1914. In the alternative, pivot rack1912 may be movably attached to pivoting link 1914 to provide additionalself-alignment. This may be accomplished, for example, by having any oneor more bores used to fasten pivot rack 1912 be formed as slots orformed as bores significantly larger than fasteners passingtherethrough. The pivot rack 1912 may have positional memory (e.g.,provided by a spring or other biasing member) in any one or moredirections or orientations and may be “floating” in any one or moredirections or orientations, as discussed herein. Pivoting link 1914 ispivotally attached to the frame 1911 at pivot point D via fastener 1920and operatively connected to rear pivot arm 2102 at point C via fastener1922. As indicated by the arrows in FIG. 24, rotation of rear pivot arm2102 about pivot point B causes pivot link 1914 to pivot about pivotpoint D, causing pivot rack 1912 to move into or out of contact withmotor rack 1930. A rack bracket 1932 is utilized for attaching eachmotor rack 1930 to each front pivot arm 1956.

Similar to pivot rack 1912, and as previously described, one side ofmotor rack 1930 includes a series of ratchets or teeth that engage theteeth on the pivot rack 1912 when both components are properly orientedand stabilization system 1910 is in operation. In the exemplaryembodiment, motor rack 1930 is movably attached to rack bracket 1932 byshoulder screws 1934, 1936 fastened through bracket 1932 to threadedbores 2134, 2136 (FIGS. 21A-21B) in motor rack 1930. Shoulder screws1934, 1936 do not tightly fasten the motor rack 1930 to the bracket1932; rather, the shoulder screws 1934, 1936 engage correspondingshoulders in corresponding bores 2134, 2136 so that the motor rack 1930essentially hangs from bracket 1932, leaving a slight gap between thetop surface of motor rack 1930 and the bottom surface of rack bracket1932 (see FIGS. 25A-25B and 27). Thus, the motor rack 1930 is free tomove up and down. Additionally, the motor rack can move laterally. Morespecifically, as shown in FIG. 26, a slot 1939 is formed through rackbracket 1932, with shoulder screw 1936 extending through slot 1939. Slot1939 provides the motor rack 1930 with the ability to move laterally tosome extent (i.e., the ability to rotate back and forth about a pivotpoint created by shoulder screw 1934). A washer 1937 between shoulderscrew 1936 and bracket 1932 provides a larger sliding surface as themotor rack 1930 moves back and forth, and provides a desired angle ofthe motor rack 1930 relative to the other locking member 1912. Mountingmotor rack 1930 to rack bracket 1932 in the described manner allowsmotor rack 1930 to “float” as it hangs off of the bracket 1932 to whichit is mounted. In the exemplary embodiment, a biasing member orcompression spring 1938 is mounted between motor rack 1930 and bracket1932 inside bore 2138 (FIGS. 21A-21B) and confers a degree of positionalmemory to motor rack 1930. More specifically, spring 1938 biases themotor rack 1930 against a surface of the bracket 1932 so that therelative position of the motor rack 1930 during an engagement with theother locking member 1912 with respect to slot 1939 will be maintainedafter disengagement, and the motor rack 1930 also remains movablyconnected to the bracket 1932 permitting the motor rack 1930 toself-align in that slot for the next engagement, if necessary. In thespecific embodiment shown, even though the spring 1938 causes the motorrack 1930 to have positional memory with respect to slot 1939, the motorrack 1930 is free to move up (e.g., rotate up) against the spring witheach engagement with the other locking member 1912 and move down (e.g.,rotate down) with each disengagement with the other locking member 1912via the freedom of movement provided by shoulder screw 1934. Althoughmotor rack 1930 is shown in the figures as being mounted from its top,motor rack 1930 (and pivot rack 1912) may be mounted in a manner otherthan as specifically shown. For example, motor rack 1930 may be movablymounted from its side via a bore and a slot and/or a pair of slots.

With specific reference to FIGS. 23-24, pivot rack 1912 and motor rack1930 are triggered to engage each other whenever rear caster 2100 islifted from (or about to be lifted from) its supporting surface (i.e.,when one or both of the rear casters 2100 are “unloaded”), such as whenthe wheelchair's user leans significantly forward or perhaps on certainsurfaces. That is, motion of the frame 1911 relative to the rear pivotarm 2102 permits the caster-end of the rear pivot arm to drop under theforce of gravity. From the perspective of FIGS. 19, 23, and 24, the rearpivot arm 2102 drops (i.e., rotates counterclockwise in those figures)responsive to being unloaded. Right rear pivot arm 2102 a in FIG. 19 isshown as having dropped, causing right pivot rack 1912 a to move forwardto engage right motor rack 1930 a. Left rear pivot arm 2102 b and leftmotor pivot rack 1912 b are shown in the neutral position in FIG. 19 inwhich the lock is not engaged. The pivot link 1914 is pivotallyconnected to the frame at pivot point D and connected to the rear pivotarm at pivot point C. Thus, the relative motion between the frame andthe rear pivot arm 2102 as the rear pivot arm is unloaded causes thepivot link 1914 to rotate in an opposite direction about its pivotalconnection at pivot point D so that the pivot rack 1912 at the end ofpivot link 1914 comes into contact with and engages motor rack 1930.When pivot rack 1912 engages motor rack 1930, the front pivot arm 1956and rear pivot arm 2102 engage, which prevents any additional motion ofthe frame 1911 relative to the front pivot arm 1956 in that direction,which will tend to prevent any further tipping in that direction. Whenthe wheelchair frame 1911 moves back in the opposite direction, so thatthe rear casters are re-loaded and pushed back up, the pivot rack 1912disengages the motor rack 1930, which permits the front pivot arm 1956to once again freely pivot about pivot point A. More specifically,motion of the frame 1911 relative to the rear pivot arm 2102 in theopposite direction causes the pivot link 1914 to move in the oppositedirection, which causes pivot rack 1912 to disengage from motor rack1930, which permits the front pivot arm 1956 to freely pivot about pivotpoint A.

In the exemplary embodiment shown in the figures, there are twoindependent stabilization systems installed on frame 1911; one on theright side and the other on the left side. Thus, if an uneven surfaceencountered by the user of the wheelchair causes only one of the rearpivot arms to drop or rotate at pivot point B, the engagement of justone of the stabilization systems will typically be adequate to preventthe chair from tipping over in a forward direction.

The motor rack 1930 is essentially self-aligning with respect to thepivot rack 1912. Such self-alignment is the result of the movableconnection between motor rack 1930 and the front pivot arm 1956 via thebracket 1932. In the specific embodiment shown, the motor rack 1930 hasfreedom of motion in several directions (the motor rack 1930 is capableof a certain degree of lateral rotation and vertical freedom of movementrelative to front pivot arm 1956 (and ultimately freedom of movementrelatively to pivot rack 1912)). This self-aligning characteristic mayhelp compensate for various factors, such as component wear patterns,user weight, deformations as a result of collisions, and other factors,any one or more of which may cause the pivot rack 1912 and motor rack1930 to be horizontally offset from nominal alignment and/ornon-coplanar and/or vertically offset from nominal alignment. Someoverlap between the two racks 1912, 1930 will permit self-alignment ofthe motor rack 1930 relative to the pivot rack 1912 and perhaps resultin sufficient overlap between the two racks 1912, 1930 to help preventtipping, as discussed above. In the exemplary embodiment, the ratchetedor toothed side of the pivot rack 1912 is significantly longer than thatof the motor rack 1930, thereby providing multiple engagement pointsalong its length (see FIG. 25). Thus, the relative vertical alignment ofthe two components need not be exact for effective engagement of thepivot rack 1912 and the motor rack 1930. Accordingly, precise lengthwiseand widthwise alignment is not required for effective engagement or“locking” of these components. Additionally, in the exemplary embodimentshown, the motor rack 1930 and the pivot rack 1912 may be spaced furtherapart than other embodiments of this invention, e.g., spaced apart byabout a half-inch or more.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. For example, pivotal connections can be madeof any number of structures including bearing assemblies, pins, nuts andbolts, and frictionless sleeve assemblies. Additionally, springs orshock absorbers can be added between pivoting and non-pivotingcomponents to limit, dampen, or somewhat resist the pivotal motions ofthese components. Also, a brake-disc locking mechanism could beintegrated into pivotal connection 406 that locks pivotal connection 406from rotation when actuated and freely allows pivotal motion aboutconnection 406 when not actuated. Therefore, the invention, in itsbroader aspects, is not limited to the specific details, therepresentative apparatus, and illustrative examples shown and described.Accordingly, departures can be made from such details without departingfrom the spirit or scope of the applicant's general inventive concept.

The invention claimed is:
 1. A wheelchair suspension comprising: aframe; a pivot arm pivotally coupled to the frame; a front castercoupled to the pivot arm; a rear caster pivotally coupled to the frame;a stabilizing system coupled to the frame and the pivot arm; a sensorcoupled to the stabilizing system; the sensor being arranged such thatmovement of the frame relative to the rear caster causes actuation ofthe stabilizing system to at least partially resist further movement ofthe frame.
 2. The wheelchair suspension of claim 1 wherein actuation ofthe stabilizing system at least partially resists movement of the frontcaster relative to the frame.
 3. The wheelchair suspension of claim 1wherein the sensor comprises a cable that is coupled to the rear casterand the frame.
 4. The wheelchair suspension of claim 1 wherein thestabilizing system comprises a reciprocating rod and a valve.
 5. Thewheelchair suspension of claim 1 wherein the sensor actuates thestabilizing system when the frame moves upward relative to the rearcaster.
 6. The wheelchair suspension of claim 1 wherein actuation of thestabilizing system inhibits at least upward movement of the front casterwith respect to the frame.
 7. The wheelchair suspension of claim 1wherein the sensor comprises a cable and a pivot bracket.
 8. Thewheelchair suspension of claim 1 wherein the sensor comprises a cableand a pivot bracket that is coupled to the rear caster such that thesensor actuates the stabilizing system when the frame moves upwardrelative to the rear caster.
 9. The wheelchair suspension of claim 1wherein the suspension assembly includes a second front caster coupledto a second pivot arm, wherein actuation of the stabilizing systemsimultaneously resists movement of the first and second pivot armsrelative to the frame.
 10. The wheelchair suspension of claim 1 whereinactuation of the stabilizing system at least partially resists movementof the front caster relative to the frame in a first direction andallows movement of the front caster relative to the frame in a seconddirection.
 11. The wheelchair suspension of claim 1 wherein thestabilizing system comprises a spring assembly.
 12. The wheelchairsuspension of claim 11 wherein the spring assembly comprises a gasspring.
 13. The wheelchair suspension of claim 11 wherein the springassembly comprises a hydraulic spring.
 14. A wheelchair suspensioncomprising: a frame; a front caster; a first pivot arm and a secondpivot arm pivotally coupled to the frame and the front caster; a rearcaster pivotally coupled to the frame; a stabilizing system coupled tothe frame and at least one of the first and second pivot arms; a sensorcoupled to the stabilizing system; the sensor being arranged such thatmovement of the frame relative to the rear caster causes actuation ofthe stabilizing system to at least partially resist further movement ofthe frame.
 15. The wheelchair suspension of claim 14 wherein actuationof the stabilizing system at least partially resists movement of thefront caster relative to the frame.
 16. The wheelchair suspension ofclaim 14 wherein the sensor comprises a cable that is coupled to therear caster and the frame.
 17. The wheelchair suspension of claim 14wherein the sensor actuates the stabilizing system when the frame movesupward relative to the rear caster.
 18. The wheelchair suspension ofclaim 14 wherein actuation of the stabilizing system inhibits at leastupward movement of the front caster with respect to the frame.
 19. Thewheelchair suspension of claim 14 wherein the sensor comprises a cableand a pivot bracket.
 20. The wheelchair suspension of claim 14 whereinthe sensor comprises a cable and a pivot bracket that is coupled to therear caster such that the sensor actuates the stabilizing system whenthe frame moves upward relative to the rear caster.
 21. The wheelchairsuspension of claim 14 wherein the suspension assembly includes a secondfront caster, wherein actuation of the stabilizing system simultaneouslyresists movement of the first and second front casters relative to theframe.
 22. The wheelchair suspension of claim 14 wherein actuation ofthe stabilizing system at least partially resists movement of the frontcaster relative to the frame in a first direction and allows movement ofthe front caster relative to the frame in a second direction.
 23. Thewheelchair suspension of claim 14 wherein the stabilizing systemcomprises a spring assembly.
 24. The wheelchair suspension of claim 23wherein the spring assembly comprises a gas spring.
 25. The wheelchairsuspension of claim 23 wherein the spring assembly comprises a hydraulicspring.
 26. The wheelchair suspension of claim 14 wherein thestabilizing system comprises a reciprocating rod and a valve.
 27. Awheelchair comprising: a frame; a seat supported by the frame; first andsecond pivot arms pivotally coupled to the frame; first and second drivewheels coupled to the first and second pivot arms respectively; firstand second front casters coupled to the first and second pivot armsrespectively; at least one rear caster pivotally coupled to the frame;at least one stabilizing system coupled to the frame and at least one ofthe pivot arms; a sensor coupled to the stabilizing system; the sensorbeing arranged such that movement of the frame relative to the rearcaster causes actuation of the stabilizing system to at least partiallyresist further movement of the frame.
 28. A wheelchair suspensioncomprising: a frame; a pivot arm pivotally coupled to the frame; a frontcaster coupled to the pivot arm; a rear caster pivotally coupled to theframe; a stabilizing system coupled to the frame and the pivot arm; asensor coupled to the stabilizing system; the sensor being arranged suchthat movement of the frame relative to the rear caster causes actuationof the stabilizing system to at least partially resist further movementof the frame.
 29. A wheelchair suspension comprising: a frame; a pivotarm pivotally coupled to the frame; a front caster coupled to the pivotarm; a rear caster pivotally coupled to the frame; a stabilizing systemcoupled to the frame and the pivot arm; a sensor means for selectivelyactuating the stabilizing system; the sensor means being arranged suchthat movement of the frame relative to the rear caster causes actuationof the stabilizing system to at least partially resist further movementof the frame.
 30. A wheelchair suspension comprising: a frame; a pivotarm pivotally coupled to the frame; a front caster coupled to the pivotarm; a rear caster coupled to the frame; a stabilizing means; a sensorcoupled to the stabilizing means; the sensor being arranged such thatmovement of the frame relative to the rear caster causes actuation ofthe stabilizing means to at least partially resist further movement ofthe frame.
 31. The wheelchair suspension of claim 30 wherein actuationof the stabilizing means at least partially resists movement of thefront caster relative to the frame.
 32. The wheelchair suspension ofclaim 30 wherein actuation of the stabilizing means resists movement ofthe front caster upward relative to the frame and allows downwardmovement of the front caster relative to the frame.
 33. The wheelchairsuspension of claim 30 wherein the sensor is coupled to the rear casterby a cable.
 34. The wheelchair suspension of claim 30 wherein thestabilizing system is actuated when the rear caster pivots downwardrelative to the frame.
 35. A wheelchair suspension comprising: a frame;a front caster; a first pivot arm and a second pivot arm pivotallycoupled to the frame and the front caster; a rear caster pivotallycoupled to the frame; a stabilizing means; a sensor coupled to thestabilizing means; the sensor being arranged such that movement of theframe relative to the rear caster causes actuation of the stabilizingmeans to at least partially resist further movement of the frame. 36.The wheelchair suspension of claim 35 wherein actuation of thestabilizing means at least partially resists movement of the frontcaster relative to the frame.
 37. The wheelchair suspension of claim 35wherein actuation of the stabilizing means resists movement of the frontcaster upward relative to the frame and allows downward movement of thefront caster relative to the frame.
 38. The wheelchair suspension ofclaim 35 wherein the sensor is coupled to the rear caster by a cable.39. The wheelchair suspension of claim 35 wherein the stabilizing systemis actuated when the rear caster pivots downward relative to the frame.40. A wheelchair comprising: a frame; a seat supported by the frame;first and second pivot arms pivotally coupled to the frame; first andsecond drive wheels coupled to the first and second pivot armsrespectively; first and second front casters coupled to the first andsecond pivot arms respectively; at least one rear caster pivotallycoupled to the frame; at least one stabilizing means; a sensor coupledto the stabilizing means; the sensor being arranged such that movementof the frame relative to the rear caster causes actuation of thestabilizing means to at least partially resist further movement of theframe.